The present invention relates to a method of connecting and disconnecting the modules of air insulated switchgear, and a busbar system for enabling high voltages and/or high current strengths to be used in air insulated switchgear with a high degree of safety, for instance.
Air insulated switchgear intended for high voltagesxe2x89xa71 Kv and high current strengths are often equipped with flat busbars that have a high copper content and preferably a rectangular cross-section. The cross-sectional surface area of a busbar and its distance from another conductive material must be dimensioned in accordance with the voltage/current strength levels so that losses will be small and the risk of flashover reduced. Thus, in high voltage plants of the switchgear kind, a busbar system having a rectangular cross-section may require a relatively large amount of space in order to prevent the occurrence of flashover. The busbars are joined and connected by means of screw/nut joints, therewith creating contact surfaces between the busbars and respective jointing means. Conventional busbar systems are most often assembled and fitted by mechanics or like artisans, and the work involved is relatively laborious and time-consuming. AS a result, the work necessitated in connecting and disconnecting switchgear modules is complicated, time-consuming and dependent on the services of an artisan or mechanic.
With the intention of reducing the space requirements of air insulated switchgear having a busbar system for high voltages/high current strengths and simplifying jointing and connection of the busbar system and therewith simplifying the manufacture and fitting of the system, the busbars of the busbar system have been given the form of tubes which, when applicable, have welded/soldered thereto tubular connectors for connecting the system to contact breaker connections. The insertion end of one busbar tube has fitted on its insertion end an electrically conductive contact element in the form of an annular coil spring which is received and affixed in the receiving end of another busbar tube configured to this end, therewith enabling the tubular cylindrical busbar to be easily joined/connected together. As the spring-carrying insertion end of said busbar tube is inserted into the receiving end of the other tube, the spring is compressed and therewith exerts a pressure and holding force between the tubes while remaining in a compressed state. The coupling and holding force exerted between the insertion end of the one tube and the receiving end of the other tube can be improved by providing a groove in the inner surface of the said receiving end of the other tube, so that the spring is able to expand to some extent. The spring provides a large number of contact points with each tube end, therewith providing an efficient tube coupling and an essentially loss-free contact for electrical transmission purposes. A contact which is stable over a long period and with which the minimum of oxidation occurs can be obtained by protecting the contact points from the surrounding atmosphere with the aid of seals on both sides and by optionally greasing the enclosed volume. The use of tubes in air insulated switchgear enables the busbars to be disconnected cabinet-wise/unit-wise and also enables coupling means in the main current path to be removed without needing to loosen or remove fixed connections in the busbar system. Thus, in the assembly of switchgear different switchgear modules can be readily connected together by pushing the insertion ends of respective tubular busbars into the corresponding receiving ends of juxtaposed tubular busbars.
According to another embodiment of the present invention, there is used a tubular jointing element which is mounted on the outer ends of the tubular busbars. The jointing element may have the form of a tube provided with an electrically conductive contact element in the form of a ring-shaped coil spring fixed on the outer side of the jointing element, one coil spring at each end. The tubular busbars are joined together by pressing the spring-carrying jointing element into the tubular busbars to be joined together, therewith compressing the springs, which remain compressed and exert a pressing and holding force between the tubular busbars and the jointing element. The coupling strength and retaining strength of the joint can be improved by providing a groove on the inner surface of respective tubular busbars, so as to enable the springs to expand to some extent.
The jointing element may also have the form of a tube which includes an electrically conductive contact element in the form of a ring-shaped coil spring fixed on the inside of the jointing element, one coil spring at each end. In this case, the tubular busbars are pressed into the jointing element, therewith compressing the springs.
The joints produced in accordance with the present invention give a greater degree of reliability than conventional bolt joints, because they eliminate the risk of human error involved with earlier used bolt connections.
In the case of a tubular busbar system in air insulated switchgear intended for high voltages and high current strengths, the spacing between respective busbars can be made smaller than the spacing between the rectangular busbars of conventional busbar systems having rectangular cross-section with the same quantity of material per unit length, therewith obtaining switchgear with smaller outer dimensions. As a result of the skin effect among other things, i.e. the phenomenon by which high frequency currents tend to be confined to the thin skin of conductors, tubular busbars are able to conduct more current than a homogenous busbar having the same cross-sectional surface area, at the same time as the electrical power field becomes weaker around the busbar. The xe2x80x9celectrodexe2x80x9d effect that is liable to be obtained with conventional busbars and result in flashover is not obtained with a round busbar. The round shape is also retained in the joints when practicing the inventive jointing technique. Neither will soldering and welding of copper tubes with the aid of present-day techniques result in weakenings or negatively effect the electrical conductivity; on the contrary, the electrical resistance may be reduced in the region of the connection by the solder/weld.
Cooling air can be circulated through the tubular busbars of the described busbar system, either by forced circulation with the aid of a fan, or by natural circulation with the aid of upwardly and downwardly angled terminating means at both ends of the busbar system.